# TikZ: Labeling an angle does not work in my case

I'm trying to draw a simple coordinate system using TikZ. I've also got an angle which I want to label as phi (\varphi). The following code without the label works:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{tkz-euclide}
\usetikzlibrary{positioning,calc,patterns,angles,quotes}

\definecolor{grid-light-grey}{gray}{.95}

\begin{document}

\frame{
\begin{tikzpicture}[axis/.style={very thick, ->, >=stealth'}]
\tkzInit[xmax=5, ymax=3, xmin=-2, ymin=-2]
\tkzGrid[sub, color=grid-light-grey, subxstep=1, subystep=1]

%% CUSTOM AXIS
\draw[axis] (-2.5, 0) -- (5.5, 0) node(re)[below left] {$Re$};
\draw[axis] (0, -2.5) -- (0, 3.5) node(im)[below left] {$Im$};
\coordinate (origin) at (0,0);

\draw[draw=green, thick] (origin) -- (3, 2)  node [anchor=south west] {$z = a + bi$}
node[] (num) {\fontfamily{qag}\selectfont x};

\draw[dashed] (3,  2) -- (0,  2) node[anchor=east] {$b$};

\draw[dashed] (3,  2) -- (3,  0) node[anchor=south west] {$a$};

\node[color=green] at (1, 1) {$r$};

\pic[draw] {angle = re--origin--num};
\end{tikzpicture}
}

\end{document}


Unfortunately, when I try to label the angle by passing an option to the \pic command:

\pic[draw, "$\varphi$"] {angle = re--origin--num};


Suddenly it leads to an error. This is especially peculiar since the same setup seems to work in this answer to a similar question:

https://tex.stackexchange.com/a/219039/172626

Does anybody see what the problem is, and why the syntax works in the answer to that question, but not in my case?

• What error you got? I get no error here. – Sigur Oct 21 '18 at 12:24
• I'm sorry, I should have checked the minimal example before posting. Apparently, it's an error that only occurs within my bigger document. To avoid it, I'll just compile the image in a different text document and include the pdf. – R. Hahnemann Oct 21 '18 at 12:28
• Does adding \usetikzlibrary{babel} to the preamble of the big document help? – user121799 Oct 21 '18 at 16:21

I've encountered the problem again, and I've tried out @marmot's advice on including the tikzlibrary babel. The problem is indeed solved.